Orthodontic treatment is effected by fixing small appliances often referred to as orthodontic brackets to a patient's teeth in an appropriate manner so as to correct malaligned teeth by applying an external force thereto through an archwire extending between the generally fixed orthodontic brackets. Directions mesial and distal mean generally left to right. Labial is the front surface, while lingual is defined as anything toward the direction of the tongue and it thereby stands to reason the word lingual is definitively and additionally defined as behind the labial surface. As to the structure of these orthodontic brackets, they are constructed of a body having small slots and are adhered directly on the labial or lingual sides of the teeth or welded to metal bands attached to the teeth by cementing or by some other method, as is generally known in the art.
As the form of use of the orthodontic bracket constructed as described above, a flexible archwire, which is curved so as to conform to a dental arch, is placed in an archwire slot in the bracket, and the tooth can be shifted over time by the restoring force of the archwire so that the teeth become well aligned. With the orthodontic bracket, a force can be applied to the tooth in a desired direction to correct the direction in which the tooth is shifted, rotated, tipped or torqued. This is effected by the three-dimensional inclination of the slot formed in the bracket body or by the desired bending of the archwire. Light, continuous forces are desirable for ideal biological movement that also reduce the risk of root resorption (root shortening).
Orthodontic treatment is accomplished by transmitting the restoring force of the archwires through brackets to the tooth roots. Generally, in an early period of the treatment, a thin, highly flexible round archwire is used, and an operation is required to loosen the ligature wire after ligating it such that the round wire freely slides within the slot (on a very low frictional basis). As treatment progresses, a thicker wire, a square or rectangular wire, and a more highly rigid wire eventually is used. When the alignment is nearly completed, the teeth are held for a while to prevent relapse. At this time, there are cases where the tooth is strongly fastened by a ligature wire so that it practically does not shift.
Various types and designs of self-ligating brackets are known in the art that provide different advantages, or solve particular problems depending on the patient's oral physiology. One type of self-ligating bracket uses a slider mechanism, such as a flat cap or plate that slides lineally within grooves or guides, to retain the archwire in the archwire slot. At one end of the slider mechanism's range, the archwire slot is closed and at the other, it is open. Any of a variety of structures can be used to bias or retain the slider mechanism in its open or its closed position. The invention provides an improvement to this type of passive self-ligating bracket.
One example of this type of bracket is shown in U.S. Pat. No. 6,168,428 to John Voudouris issued Jan. 2, 2001, and specifically at FIGS. 48 to 52. In this bracket, a spring member in the form of a resilient shim 720 located lingually to the labial face of the bracket, projects gingivally and has a jog directed lingually toward the archwire slot 3240d and presents a generally convex surface 722 towards the archwire slot 3240d. The gingival edge 724 of the shim 720 recurves labially.
As the arms 3540 slide within the slots 3530 to move the clip 3538 to a closed position as shown in FIG. 49, the convex surface 722 of the shim 720 engages the archwire 3242d and provides a continuous biasing action against the archwire. As may be seen in FIG. 51, the resilience of the shim 720 allows the orthodontic bracket 3220d to accommodate different sizes and configurations of archwires 3242d while maintaining a continuous action against the archwire.
One of the problems associated with this passive, straight clip design is that the archwire is loose within the archwire slot.
One modification of the Voudouris patent, to aide in the problem the passive clip resulting in looseness of the archwire in the slot mentioned above is addressed by United States Patent Publication No. 2011/007663 published Mar. 31, 2011 to Bryant et al. This application provides for a slidable shim member (referred to therein as clip 20 shown in FIG. 1) slidable into two outer tracks extending in an occlusal-gingival direction on the outer lateral surfaces of the bracket, with a vertical trough extending in an occlusal-gingival direction between the outer tracks. The shim has two parallel outer arms and a central tongue between the outer arms. The outer tracks of the bracket slidably engage the outer arms of the clip and the central tongue is slidably engaged by the vertical trough of the bracket, thereby allowing the clip to slidably move between an open position in which the outer arms of the clip are retracted and a closed position in which the outer arms of the clip extend across the archwire slot to retain the archwire in the archwire slot.
One problem associated with the Bryant et al. disclosure is that the shim prevents movement of the archwire out of the archwire slot, but, depending on the size of the archwire being used, the shim generally is not in contact with the archwire and thus there is still movement or looseness of the archwire within the archwire slot, as is illustrated in FIG. 5 of this disclosure. This results in a lower torque being applied to the archwire by the bracket overall as there is typically no contact between the shim and the archwire.
There is therefore a need in the art for a self-ligating orthodontic bracket having active archwire retention that addresses one or more of the aforementioned problems with the prior art.